This project seeks to investigate comparative efficacy of monoamine oxidase inhibitors in neurotic depression; existence of patient subtypes; differential response in such subtypes; pharmacological factors affecting response. A controlled clinical trial will be carried out in outpatients and day hospital patients showing neurotic depression or mixed anxiety depression of mild to moderate severity. After an initial week on placebo patients will be assigned randomly to phenelzine, amitriptyline or placebo and treated for six weeks. A variety of symptom rating scales will be employed as outcome measures, supplemented by social and psychiatric history predictors at initial rating. Typological and regressional methods will be used to develop predictors. Platelet MAO inhibition will be monitored. Genetic polymorphism with respect to fast or slow acetylation will be determined pretreatment and its relation to response, diagnosis, and degree of MAO inhibition examined.